datatype/Interpreter.hs

   1 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
   2 {-# LANGUAGE FlexibleInstances #-}
   3 {-# LANGUAGE MultiParamTypeClasses #-}
   4 module Interpreter where
   5
   6 import Language
   7 import Control.Monad
   8
   9 newtype Interpreter a = I {runInterpreter :: Maybe a}
  10   deriving (Functor, Applicative, Monad)
  11
  12 instance Expression Interpreter where
  13     lit = pure
  14     (+.) = liftM2 (+)
  15     (-.) = liftM2 (-)
  16     (/.) = liftM2 (/)
  17     (*.) = liftM2 (*)
  18     neg = fmap negate
  19     (&.) = liftM2 (&&)
  20     (|.) = liftM2 (||)
  21     not = fmap Prelude.not
  22     (==.) = liftM2 (==)
  23     (/=.) = liftM2 (/=)
  24     (<.) = liftM2 (<)
  25     (>.) = liftM2 (>)
  26     (<=.) = liftM2 (<=)
  27     (>=.) = liftM2 (>=)
  28     if' p t e = p >>= \b->if b then t else e
  29
  30 instance Function a Interpreter where
  31     fun def = Main $ let g :- m = def g in unmain m